The construction of pipelines generally involves the axial connection of two lengths of pipe to form a single pipeline conduit for transporting materials from one point to another. Along the pipeline there may be one or more fittings, which allow the pipe pieces to be joined to other components in the pipeline. The materials usually conveyed via pipelines require that pipeline conduits and joints between axially-joined pieces of pipe, and between pipes and fittings, be substantially leak-proof.
Some applications require that the joints between pipe components are restrained in some manner. This is usually desired in order to prevent the pipe components from separating due to thrust forces that often occur when the pipeline is subjected to internal pressure, and sometimes, when earth tremors or other external events occur. A challenge is to make the assembly of the pipe joints as simple, economical, and reliable as possible. Due to this, the industry has focused substantial attention on the problem of maintaining connections between adjacent lengths of pipe after installation. The result of this attention is a variety of differing designs and approaches known in the art. The majority of these designs can be categorized into either “mechanical joints” or “push-on joints.”
The term “pipe” as used herein shall be understood to include pipe sections, fittings, connections, and any other appurtenances to pipes.
One of the well known and the most common sealing systems used in the industry is referred to as a “mechanical joint” or simply as “MJ”. The bell end of one pipe has a cast flanged portion that is capable of receiving an elastomeric gasket. A male piping member (spigot end) of a second pipe is fitted with an elastomeric gasket and gland fitting. The fitting and the bell flanged portion have a plurality of apertures for receiving standard bolts. Before assembling the MJ connection, the fitting and the elastomeric gasket are placed over the spigot end of the second pipe. A pressure tight joint is formed when the spigot is axially inserted into the bell, and the fitting and the bell flanged portion are bolted together causing the fitting to compress the elastomeric gasket, thus sealing the two pipe pieces.
The MJ connection enjoys wide acceptance in the industry, and is the subject of national and international Standards such as ANSI/AWWA C111/A21.11-95, which is incorporated in its entirety herein by reference.
Numerous attempts have been made to improve upon the standardized mechanical joint. These attempts are almost uniformly characterized by the inclusion of an additional mechanism or attachment, creating a mechanical connection that resists separation of the pipes.
Such attempts often require modification of the bell or the gland fitting (or both). Examples include designs that employ locking inserts recessed within the gland such as U.S. Pat. No. 784,400 to Howe and designs that rely upon specially modified bolts having toothed cams that both pivot on and bite into the spigot as the bolts are hooked under a modified lip of the bell and forced into grooves in the gland such as U.S. Pat. No. 1,818,493 to McWane. However, these solutions cannot be applied to the existing standardized mechanical joint bells.
Further attempts employ additional restraining devices or teeth that are driven into the spigot as the gland fitting is tightened. In some cases, these devices or teeth are interposed between the gasket and the gland. In other cases, these devices or teeth are implemented in the elastomeric gasket. Included among these devices is U.S. Pat. Nos. 4,664,426 to Ueki and 7,207,606 to Owen et al. In other cases, these devices or teeth are implemented in the elastomeric gasket. This solution may be illustrated by U.S. Pat. Nos. 7,104,573 to Copeland; 7,108,289 to Holmes et al.; and 7,125,054 and 7,410,174 to Jones. However, the assembly of these modified MJ connections still involves in-field installation of the gland, gasket, bolts, and nuts, which can be time consuming.
Another common method for connecting pipes together involves the insertion of the spigot end of the first pipe into an expanded end of the second pipe, where the interior profile of the second pipe has been specially fabricated to accommodate specially shaped elastomeric gaskets. The elastomeric gasket is sized to accommodate the spigot end of the male piping member to be received. This connection type is known in the pipe industry as a “push-on joint.” In-field assembly of the push-on connection is much simpler than the assembly of the MJ connection. It does not involve any bolts and nuts and requires less time for assembly than the MJ connection. The spigot end of the male piping member is inserted into the bell end of the second pipe, thus developing a sealing arrangement between two pieces of pipe. No follower ring, stuffing box, or other compression mechanism is typically presented in the push-on joint. Additionally, the typical push-on joint does not include a restraining mechanism, though such mechanisms as tie bars, concrete thrust blocks, screws, and additional ring attachments have been employed in some cases to provide restraining performance. Advancements in the art have led to innovations and modifications of push-on joints to include restraining rings. Examples of such restrained push-on joints include U.S. Pat. Nos. 3,963,298 and 4,229,026 to Seiler; 5,295,697 and 5,464,228 to Weber et at; and 5,067,751 to Walworth et al. In some designs, the securement of the connection is effected by locking segments spaced uniformly around the elastomeric gasket inner perimeter. The toothed segments possess a groove that mates with an annular rib on the bell, such that the rib acts as a rocker, or cam, or, during some movements, as a wedge. During insertion of the spigot into the bell, the segments rotate on the rib, but are prevented from appreciable straight-line movement by engagement of the rib and groove. Upon experiencing counter-forces tending to effect removal of the spigot, the rib acts as a cam, both causing the segments to pivot on the rib, and exerting a radially inward pressure as the segments attempt to slide past the rib. These self-restraining gaskets, however, cannot be used with the standard bells for MJ connection because of their specific shape and rib requirement.
What is needed therefore is a self-restrained pipe joint system that may be used with standard mechanical joint bell and which may possess combined advantages of the push-on and mechanical joints, such as easy in-field assembling and disassembling.